1. Field of the Invention
The present invention relates to pretreating and passivating metal substrates to provide corrosion resistance to the metal substrates which are to be subsequently coated.
2. Brief Description of the Prior Art:
It is well known in the prior art that chromic acid pretreatments passivate and improve the corrosion resistance and coating properties of metal, particularly ferrous metal substrates. However, chromic acid pretreatments are undersirable because they are toxic and their effluents create serious pollution problems. The present invention resides in the discovery that specific onium salts can be used in a passivating pretreatment process for metal substrates, particularly ferrous metal substrates. The onium salts employed in the present invention are not toxic, do not present the serious pollution problems associated with chromic acid pretreatments, and have been found to provide excellent corrosion resistance to the treated metal substrates. Subsequently coating with a layer of paint provides a metal substrate with outstanding corrosion resistance.